[PATCH v2] carl9170: tx: fix an incorrect use of list iterator

[Xiaomeng Tong <xiam0nd.tong@gmail.com>]

If the previous list_for_each_entry_continue_rcu() don't exit early
(no goto hit inside the loop), the iterator 'cvif' after the loop
will be a bogus pointer to an invalid structure object containing
the HEAD (&ar->vif_list). As a result, the use of 'cvif' after that
will lead to a invalid memory access (i.e., 'cvif->id': the invalid
pointer dereference when return back to/after the callsite in the
carl9170_update_beacon()).

The original intention should have been to return the valid 'cvif'
when found in list, NULL otherwise. So just return NULL when no
entry found, to fix this bug.

Cc: stable@vger.kernel.org
Fixes: 1f1d9654e183c ("carl9170: refactor carl9170_update_beacon")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
---

changes since v1:
 - just return NULL when no entry found (Christian Lamparter)

v1:https://lore.kernel.org/lkml/20220327072947.10744-1-xiam0nd.tong@gmail.com/

---
 drivers/net/wireless/ath/carl9170/tx.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
index 1b76f4434c06..791f9f120af3 100644
--- a/drivers/net/wireless/ath/carl9170/tx.c
+++ b/drivers/net/wireless/ath/carl9170/tx.c
@@ -1558,6 +1558,9 @@ static struct carl9170_vif_info *carl9170_pick_beaconing_vif(struct ar9170 *ar)
 					goto out;
 			}
 		} while (ar->beacon_enabled && i--);
+
+		/* no entry found in list */
+		return NULL;
 	}
 
 out:
-- 
2.17.1